Synthetic uses of steroidal ring B diene protection: 22,23-dihydroergosterol

Protection of the ring B diene system of ergosterol by (i) a two-step addition of the elements of water across the 5,6-double bond, (ii) formation of the 4-phenyl-1,2,4-triazoline-3,5-dione adduct, or (iii) formation of the iron tricarbonyl adduct by treatment with p-methoxybenzylideneacetonetricarbonyliron, allowed selective reduction of the 22,23-double bond by catalytic or, as appropriate, ionic hydrogenation. Regeneration of the 5,7-diene system in each case gave a high yield of 22,23-dihydroergosterol.